Extremely fine-disperse silicon nitride powders were prepared by ball attrition milling. Surface areas greater than 50 m2/g were achieved without reaching a milling equilibrium and a corresponding upper surface limit. The diameter of the primary particles was decreased to such an extent that distinct changes could be observed in the X-ray diffractograms of Si3N4 powders; until 20% of the amount of silicon nitride were transformed into the X-ray amorphous state. All parts of the attrition mill in contact with the charge were made of abrasion resistant materials, either of SSN ceramics (stirring arms and balls) or of polyamide plastics (jar and stirring shaft coating), in order to obtain the powders as pure as possible. In this way, additional metallic contaminations of the powder were completely avoided. In detail the composition changes of the Si3N4 powder as a function of the milling time were also analysed for the following constituents: aluminium, yttrium, carbon, nitrogen and oxygen. Some consequences are pointed out for the subsequent handling and processing of the milled powders. Moreover, additional measures are offered in order to diminish the oxygen pickup caused by reactions of the powder with air and moisture during grinding.
